There exists a need in the art for a projection lens system and, in particular, a rear projection lens system, that has some and preferably all of the following properties:
(1) The system is fully color corrected. PA1 (2) The system is a high speed system, e.g., it has an infinite conjugate f/# of 1.0. PA1 (3) The system has a wide field of view in the direction of the screen, e.g., a half field of view in the direction of the screen of at least 25.degree.. PA1 (4) The system produces a high quality image, e.g., the system has an MTF above 0.5 at 10 cycles/millimeter. PA1 (5) The quality of the image is insensitive to changes in temperature of the lens system, e.g., changes between room temperature and the system's operating temperature. PA1 (6) The system produces an image which is bright in the corners, e.g., the pupil area in the corner is at least 50% of the pupil area on axis. PA1 (7) The system is compact, i.e., its lens elements are spaced close together so that the overall system has a short barrel length. PA1 (8) The system is suitable for use with small diameter cathode ray tubes (CRTs), e.g., it can be used with 3-inch CRTs which have a diagonal of about 65 millimeters. PA1 (9) The system is economical to manufacture. PA1 (a) a negative first lens unit (U1) which comprises: (i) at least one aspheric surface and (ii) a negative lens element (E1) at the unit's image side, said negative lens element having an image side surface (S1) which is concave towards the image; PA1 (b) a positive second lens unit (U2) which comprises the following lens subunits in order from the image side: PA1 (c) a third lens unit (U3) which has a strong negative power, is associated with the CRT during use of the lens system, and contributes to the correction of the lens system's field curvature. PA1 (1) to provide a high level of aberration correction, U1 and U.sub.S2 each have two aspheric surfaces; PA1 (2) again to provide a high level of aberration correction, surface S1 is an aspheric surface; PA1 (3) to aid in the correction of field curvature, .vertline..PHI..sub.E1.vertline./.PHI..sub.0 is at least 0.15, preferably at least 0.2, and most preferably at least 0.25, where .vertline..PHI..sub.E1.vertline. is the magnitude of the power of element E1 and .PHI..sub.0 is the overall power of the lens system; PA1 (4) to provide the foregoing power level without unduly increasing the curvature of the S1 surface, E1 is preferably biconcave; PA1 (5) to provide a compact lens, D.sub.12 /f.sub.0 (or, equivalently, D.sub.12.multidot..PHI..sub.0) is less than or equal to 0.25, where D.sub.12 is the distance between the object side surface of E1 and the image side surface of U.sub.S1 and f.sub.0 is the effective focal length of the lens system (f.sub.0 =1/.PHI..sub.0); and PA1 (6) to aid in thermal compensation, U.sub.S1 is a strong lens unit and the image side lens element (E2) of U.sub.S2 has a positive power.